This invention concerns a method of forming slide gate valve parts by casting an admixture of water and a castable refractory composition into a form.
Slide gate valves are well-known devices used to control the flow of molten metal, for example steel, from a vessel such as a ladle or tundish. In these devices, a movable or sliding plate with a hole or passage for the molten metal slides or rotates into and out of registry with a hole or passage in a fixed plate attached to the vessel containing the molten metal to permit or stop the flow of metal through the passages. One typical such device is shown in U.S. Pat. No. 4,063,668.
In these devices, the fixed, so-called "upper plate", and the movable, so-called "bottom plate", each containing a hole or passage for molten metal, are the primary wear pieces and consequently have to be replaced frequently, for example after pouring one heat of steel. Accordingly, the slide gate valve must be repaired by frequently replacing these wearing parts. It is the making of these frequently replaced parts with which the present invention is concerned.
It is conventional to make these upper and lower plate parts by forming and firing refractory plates and then placing them in a bed of mortar in metal casings, the entire assembly being placed in the slide gate valve; see U.S. Pat. No. 3,841,539. After this assembly has hardened, it is necessary to grind the flat sliding surface of the assembly (in the case of a bottom plate, the surface which will be in contact with the corresponding surface of the upper plate) so as to achieve a very smooth sliding surface which will provide a tight metal-sealing joint and also to achieve the very strict dimensional tolerances required in these devices.
It has been suggested that these replacement parts be formed by casting refractory material into the metal casings, again grinding the sliding surface to achieve flatness; see French Patent Application No. 77/01683.
It is also known to place the metal casing or other form against a very smooth, almost mirrorlike, surface such as that provided by a polished metal or very smooth plastic surface, and to cast refractory material in this mold assembly, preferably using vibration to assure complete filling; see U.S. Ser. No. 930,785 filed Aug. 3, 1978. The great advantage of this method of making slide gate parts is that they can be made to great dimensional accuracy and the surface cast against the polished plate does not need to be ground prior to placing the part in service. This obviously results in lower manufacturing costs. The present invention is an improvement on this method of forming slide gate parts.
The castable refractory used in this latter method of forming parts must meet several stringent requirements: It must flow readily under vibration so as to completely fill the mold. It must be fluid enough so that any entrained air bubbles can rise to the top of the mold or to holes in the mold surface to be removed. On the other hand, it must not be so fluid that segregation of the coarse and fine particles of refractory occurs, which would lead to a poor surface. The refractory composition must form a very smooth, flat surface on the sliding face of the part. Finally, the composition must release cleanly from the highly polished plate so that there is no pitting or other flaw in the sliding surface.